1. Field of the Invention
This invention relates to a joint assembly joined capable of a click motion and a process for manufacturing the same by molding integrally, as well as to a movable body including such joint assembly and a process for manufacturing the same by molding integrally.
2. Description of the Related Art
A known joint assembly which is capable of a click motion is described in Japanese Utility Model Application KOKAI (Laid Open) No. Sho 51-47397. It comprises a core member for the thigh, a core member for a lower leg, a rivet joining the two core members rotatably, and a leg made of soft synthetic resin for covering these parts.
The known joint assembly as described above has its core member for the thigh molded in one mold, and its core member for a lower leg molded in another mold. The core members for the thigh and a lower leg have rugged parts formed at their knee ends and enabling a click motion. The core members for the thigh and a lower leg are joined together by the rivet to form a unit in which their rugged parts engage each other. The core members for the thigh and a lower leg are placed in still another mold and a soft synthetic resin material is injected for insert molding.
There is also known a joint assembly of the type including a spherical joint, as disclosed in Japanese Utility Model Application KOKAI No. Sho 50-113587. It comprises a spherical joint portion formed at the elbow (or knee) end of an upper arm (or leg), and a spherical shell portion formed at the elbow (or knee) end of a lower arm (or leg) for fitting the spherical joint portion therein.
The known joint assembly of the type including a spherical joint enables the upper and lower arms (or legs) to stay in a flexed position owing to the tight contact between the spherical joint portion on the upper arm (or leg) and the spherical shell portion on the lower arm (or leg), as the spherical joint portion is closely fitted in the spherical shell portion by virtue of the elasticity of the material of which they are made.
It has been a drawback of the known joint assembly as described before that two expensive molds have to be made for forming the two core members for the thigh and a lower leg, respectively, in two molds. The two molds have been very difficult to make, since the rugged parts enabling a click motion have to be molded in the two molds, and since no click motion is possible unless the rugged parts molded in the two molds fit each other completely.
It has also been a drawback of the known joint assembly that it is difficult to assemble, since the core members for the thigh and a lower leg have to be joined together into a unit with the rivet, and that labor is required, and its cost of manufacture is increased, since it calls for a very difficult molding process including placing the core members for the thigh and a lower leg as joined together in still another mold, and insert molding with a soft synthetic resin material.
It has been a drawback of the joint assembly of the type including a spherical joint that it is very unstable, since the upper and lower arms (or legs) which are kept in a flexed position by the tight contact between the spherical joint and shell potions, as stated before, return to their original positions immediately if their contact become less tight. In order to overcome this drawback, attempts have been made to join the spherical joint and shell portions together in a way enabling a click motion, but it has been impossible to form a rugged part in the spherical inner surface of a spherical shell portion, and even if it may be possible, it has been impossible to fit a spherical joint portion in the spherical shell portion.